Lathing lenses was the favored technique for producing rigid gas permeable lenses (RGPs). With the advent of computer numerical control (CNC) lathing contact lenses became a more viable means of mass producing lenses, although DSM (double-sided molding) processes may be the most preferred way.
Lathing may be a preferred technique for creating specialty lenses, such as lenses for presbyopia and astigmatism, or for custom lenses. As a manufacturing technique, lathing requires specific tolerances, much like any other process but tool wear/compensation may also require additional machining steps to achieve desired tolerances.
Lathing may be used to create front and/or back surfaces of lenses and/or of lens molds. In back surface lathing or machining, a blank or button may be used. The blank may be fed into a chuck to hold the button. Once the blank is held by the chuck, the spindle holding the chuck and button begins to rotate and feed or advance toward the cutting tools. Cutting tools may be made of various materials. Exemplary or preferred materials include extremely hard materials, such as diamonds and the like. The first step in lathing a lens or a mold is to lathe the blank into the proper part diameter. Next, a roughing tool may be used to cut the initial back surface geometry using a plurality of preprogrammed cuts. Typically another step is needed to make the final cuts. Each progressive path cut may be adjusted for depth and geometry by adjusting the feed or advance amount, and/or the spindle speed. The back surface of the blank/part may also be polished in any conventional manner.
After the back surface is machined, the front surface may be blocked. In this process, the part may be mounted onto a front surface tool using low melting point wax. This step of wax mounting is desirable to help avoid the potential situation wherein the back surface is not at right angles to the axis of the spindle, which may result in unwanted prism in the created mold or lens. After blocking/mounting, the front surface is lathed. Similar to the back surface lathing, the partially-finished part (button) is fixed into or onto a chuck to hold the partially-finished button. The partially-finished button must be located by the lathes, which is usually accomplished with a sensor probe that establishes the center reference point. This reference point allows a computer/controller in a computer numerical control lathe to calculate the amount the cutting tool must feed or advance in order to arrive at the required or desired center thickness of the lens.
The processes described above are typically used for symmetric designs. Oftentimes lenses and lens molds are needed that are not symmetrical, such as for example, lenses designed for presbyopia or astigmatism. These types of lenses and corresponding molds may have optical or manufacturing axes that are not the same axis as the spindle and/or the center of the lens. For example, the part may need to be cut from the point of maximum thickness, which may not be the geometric center of the part. Techniques used for creating these lenses or molds include offsetting the part such that the axis of the part aligns with the center axis of the spindle. This method is inefficient as the part must be moved multiple times to cut and finish the geometry. The present invention seeks to correct these and other deficiencies in the prior art.
As would be obvious to one skilled in the art, many variations and modifications of the embodiments found in this application may be effected without departing from the spirit and scope of the novel concepts of the disclosure.